Elsevier

Nuclear Physics A

Volume 206, Issue 2, 21 May 1973, Pages 245-272
Nuclear Physics A

The level structure of the N = 81 and 82 nucleides 137, 138Ba as investigated in 136Xe(α. xn) reactions

https://doi.org/10.1016/0375-9474(73)90531-9Get rights and content

Abstract

Alpha-particle irradiation of the enriched gaseous target 136Xe has been used to populate states in the N = 81 and 82 nucleides 137Ba and 138Ba, respectively. Singles γ-ray spectra, angular distribution, γ-γ coincidence spectra as well as time distributions with respect to the α-beam bursts have been measured at various bombarding energies. From the observed Doppler shift for some transitions an upper limit for their half-lives (T12 ≦ 70 ps) could be deduced. In 138Ba, besides the 1435.9 keV 2+, the 1898.7 keV 4+ and the 2090.2 keV 0.8 μs 6+ isomeric state observed in the radioactive decay, several high-spin, high-lying (≈ 4 MeV) states were populated. In 137Ba states were observed up to ≈ 3 MeV excitation energy, among them a newly introduced isomeric state at 2349.1 keV with possible spins (152, 172, 192). This level, which has T12 = 0.59 ± 0.10 μs, decays via a (120.2–1567.3 keV) γ-ray cascade to the well-known 2.55 min 112 isomeric state at 661.6 keV energy. The energy spacing of 138Ba is compared with theoretical predictions using δ-forces. The levels of the neutron-hole nucleus 137Ba are discussed in terms of 2p-1h and hole-vibration interactions.

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    On leave from the Institute of Nuclear Research, Swierk near Warsaw, Poland.

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